It's basically an extended Toolbar, where you can post status messages to the left of the buttons.

See the 2.2 docs for Ext.StatusBar for functionality. As I said, I didn't implement the iconCls functionality, so you can't add an image to the status bar message or show a loading indicator. For my purposes, you can setText('<img src=...> status text to be displayed') and achieve the same result, and I use other things for loading indicator (like loadMask).

The ux.StatusBar seems to be a little thinner (<height) than the
Ext2 StatusBar, you might want to increasse the default height
a little? This seems to be when you add a status bar with no
additional fields (just for text messages).

What happened to Ext.StatusBar?

I haven't upgraded to 3.0 yet. I am using the statusBar in 2.2. Does this mean the statusbar no longer works in 3.0? Can't the 2.0 statusbar (Ext.StatusBar) code be used directly in 3.0, or it needs to be re-written as you have done here.

I guess what I want to understand, is WHY does it need to be rewritten. What changed?

StatusBar is no longer supported. Search forums, there must be at least 6 threads about this.

Toolbar changed to container is one change off top of my head. But do a diff and you'll see that the old StatusBar class will no longer work from 2.x days.

I haven't examined this class to any detail, but my thought from another thread was not to have StatusBar (based on Toolbar), but maybe StatusPanel, StatusBox, StatusField or some other class that could be more easily plopped in the UI somewhere. At any rate, not sure if there's a benefit to using Toolbar as a base class...